The present invention relates to fusing machines, and, more particularly, to machines for fusing the armature wires of an electric motor to a hook member ("tang") or slot of a commutator bar and for fusing wires to stator hooks.
Although fusing machines are widely used, a system for precisely controlling the fusing operation is not yet available. Prior attempts to control the fusing operation have involved timing the period during which electric current is applied to a workpiece. However, simple timing mechanisms do not provide any feedback to the fusing machine for quality control. Other fusing machines monitor the temperature of the joint being fused with fiber optics. Temperature monitors do not indicate either electrode pressure or electrode displacement, and therefore cannot determine whether the electrode is properly deforming and fusing the armature wire and commutator.
U.S. Pat. No. 4,371,772 describes a fusing machine having a spring assembly system. A shaft moves downward to cause an electrode to contact a commutator hook. The downward movement of the shaft causes the hook to bend and compresses a spring in the fusing machine. The shaft reaches a stop, and electric current is applied. Additional force is applied by the electrode to further deform the hook and the wire to create the cohesion joint. The magnitude of the additional force will depend on the previous spring compression, the remaining spring release, and the spring's physical properties.
Even slight variations in the resistance encountered by the electrode will alter the amount of the spring's compression in the prior art system. Such variations may be caused, for example, by changes in the hook geometry, the number of wires under a hook, or variations in hook materials and wire sizes. This makes it difficult to ensure that current is applied to the electrode when there is maximum surface contact between the electrode and the hook (as required for proper operation). Successive fusing operations also depend on these variable factors, making it difficult to maintain consistency and quality control. Whenever the fusing conditions change, laborious adjustments are required to guaranty ideal current supply position and electrode force application.
The mechanical resistance of a fusion or "cohesion" joint depends on the final pressure applied. Variations in the electrode position (hook deformation) alter the heating rates and the maximum temperatures of the parts. The heating rates and maximum temperatures influence wire insulation removal, electrode wear, and the final quality of the cohesion joint.
It would be desirable to provide a fusing machine which applies electrode force in a consistent manner, tailored to the physical characteristics of the workpiece, and independent of spring compression characteristics. It would also be desirable that such a machine be able to adjust for varying fusing conditions easily and quickly.